Verification of cable application and reduced load cable removal in power over communications systems

ABSTRACT

In one embodiment, a method includes identifying insertion of a plug at a port of power sourcing equipment for delivery of Power over Ethernet, the plug connected to one end of a cable with another plug connected to an opposite end of the cable, checking for resistors at each of the plugs, determining a power rating of the cable based on the resistors located at the plugs, and powering the port to a power level based on the power rating. An apparatus is also disclosed herein.

STATEMENT OF RELATED APPLICATION

The present application claims priority from U.S. ProvisionalApplication No. 62/641,183, entitled VERIFICATION OF CABLE APPLICATIONIN POWER DISTRIBUTION OVER COMMUNICATIONS CABLING, filed on Mar. 9,2018. The contents of this provisional application are incorporatedherein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to communications networks, andmore particularly, to use of rated cable systems and online removal ofcables in power over communications systems.

BACKGROUND

Power over Ethernet (PoE) is a technology for providing electrical powerover a wired telecommunications network from power sourcing equipment(PSE) to a powered device (PD) over a link section. Conventional PoEsystems that use 90 W or less power sources are intended for safeoperation with cable systems using common connector systems. With powerover communications systems that exceed 100 W, it is important to verifyoperation of a cable for higher power PoE applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a system in which embodiments describedherein may be implemented.

FIG. 2 is a flowchart illustrating an overview of a process forverification of cable application in a power over communications system,in accordance with one embodiment.

FIG. 3 is a block diagram of a circuit for use in cable and connectorautomatic compliance verification, in accordance with one embodiment.

FIG. 4 is a table listing examples of resistor combinations that may beused to indicate cable power compatibility, in accordance with oneembodiment.

FIG. 5 is a flowchart illustrating an overview of a process for onlineremoval of a cable from the power over communications system, inaccordance with one embodiment.

FIG. 6A illustrates an example of a jack for providing status indicationof cable compatibility, in accordance with one embodiment.

FIG. 6B illustrates the jack of FIG. 6A with an online removal button,in accordance with one embodiment.

FIG. 6C illustrates a jack comprising additional status indicators, inaccordance with one embodiment.

FIG. 7 depicts an example of a network device useful in implementingembodiments described herein.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Overview

In one embodiment, a method generally comprises identifying insertion ofa plug at a port of power sourcing equipment for delivery of Power overEthernet, the plug connected to one end of a cable with another plugconnected to an opposite end of the cable, checking for resistors ateach of the plugs, determining a power rating of the cable based on theresistors located at the plugs, and powering the port to a power levelbased on the power rating.

In another embodiment, an apparatus generally comprises a cable fortransmitting power at a level exceeding 100 watts and data from powersourcing equipment to a powered device and plugs at each end of thecable, each of the plugs comprising at least one resistor. Powercapacity of the cable is identified at a port receiving one of the plugsbased on the resistors.

In yet another embodiment, an apparatus generally comprises a port forreceiving a plug connected to one end of a cable with another plugconnected to an opposite end of the cable for use in a Power overEthernet system delivering power at a level exceeding 100 watts, anonline removal button on a face of the port for use in indicating anintent to remove the plug from the port, and an online removal modulefor detecting activation of the online removal button and reducing poweron the cable to least 90 watts to prevent damage during removal of thecable.

Further understanding of the features and advantages of the embodimentsdescribed herein may be realized by reference to the remaining portionsof the specification and the attached drawings.

Example Embodiments

The following description is presented to enable one of ordinary skillin the art to make and use the embodiments. Descriptions of specificembodiments and applications are provided only as examples, and variousmodifications will be readily apparent to those skilled in the art. Thegeneral principles described herein may be applied to other applicationswithout departing from the scope of the embodiments. Thus, theembodiments are not to be limited to those shown, but are to be accordedthe widest scope consistent with the principles and features describedherein. For purpose of clarity, details relating to technical materialthat is known in the technical fields related to the embodiments havenot been described in detail.

Conventional PoE (Power over Ethernet) (e.g., 90 W and less) is intendedfor safe operation over 22 AWG (American Wire Gauge) to 26 AWG cablesystems using common RJ45 connector systems. The maximum power deliverycapacity of standardized PoE is approximately 90 watts (W), but manyclasses of powered devices would benefit from power delivery of greaterthan 100 W. Conventional PoE systems do not provide for cabledistinction that would verify operation of a cable for higher than 90 Wapplications. For PoE applications exceeding 100 W, there is a need toverify compliance of cable and connector systems. For example, in higherpower systems, such as those using 300 W PoE power supply equipment,different cable and connector systems and methods for testingcompatibility of the cable and connector are needed.

Another issue with higher power PoE systems operating at power levelsover 100 W is the current at the connector during removal of a cable.The PoE jack may operate, for example, with a per pin ampacity that cango from 500 ma to 2000 ma nominal. If the plug is removed from the jackwhile under load significant damage may occur at the connector.

The embodiments described herein provide for the use of rated cablesystems in applications using power at a level higher than used inconventional managed PoE applications (e.g., greater than 90 W). One ormore embodiments provide an apparatus, system, or method for identifyingthat the correct cable/connector assembly is used for delivered power onthe PoE port. In one or more embodiments, the delivered power may beadjusted to a lower level appropriate for the cable system if the portis unable to identify the maximum operating parameters for thecable/connector assembly. In another embodiment, a reduced load cableremoval apparatus and method provide termination of current to allow forsafe removal of the cable and plug from a powered jack.

Referring now to the drawings, and first to FIG. 1, an example of amodular transport system that may utilize power over communicationscabling (also referred to herein as enhanced PoE) for power distributionat higher power levels (e.g., ≥100 watts) is shown. The modulartransport system shown in FIG. 1 includes a dual route processor (RP)card chassis 10 supplying control and power to three line card chassis11. The dual RP card chassis may be, for example, a two RU (rack unit)chassis. The route processor card chassis 10 comprises two routeprocessors 13 (RP0, RP1), each comprising twenty downlink ports 14, adual port ground system 15, and two combination power supply unit (PSU)and fan tray modules 16 (PSU/FT0, PSU/FT1). The scalable transportsystem may support, for example, up to twenty redundant line cardconnections or eighteen line card connections and two fabricconnections. Each downlink port 14 may support, for example, integrated1 Gb/s or 10 Gb/s with a 300 W power system. The downlink ports 14supply control (data) and power to each line card chassis 11 (or fabricchassis).

In one example, the power supply units 16 provide dual 2 kW AC or DC (orother power level) redundant power modules (1+1). Each line card chassis11 comprises a line card 12 (LC0, LC1, LC2) comprising, fan tray 18(FT0, FT1, FT2), a ground system 19, and dual uplink ports 20. Power anddata are transmitted from ports 14 at the route processors 13 to theports 20 at the line cards 12 via cables 17. In this example, the routeprocessor 13 operates as the PSE (Power Sourcing Equipment) and the linecards 12 are the PDs (Powered Devices) in the PoE distribution system.

In one embodiment, the ports 14, 20 comprise interconnect ports thatcombine data and PoE utilizing an RJ45 (or similar connector). Forexample, the cable and connector system may comprise RJ45 cat7 style,four-pair communications cabling. The ports (jacks) 14, 20 may belabeled to identify capability for power exceeding 90 W. In one example,the cable and connector system may support ampacity per pin or wire to2000 ma minimum. For example, 22 AWG wire may be used to support 1500ma-2000 ma per wire in a cat7/cat5e cable system. In one example, thesystem may support a cable length of up to 15 meters (based ontechnology of cat7 cable, 22 AWG at 300 W). In one or more embodiments,the internal PSE power supply voltage may operate in the 56V to 57Vrange, 57V to 58V range, or 56V to 58V range. For example, the outputvoltage at the PSE may be 57V with an input voltage at the PD of 56V.For a 15 meter cable, a 56V power supply at the PSE can deliverapproximately 300 W power.

The terms high power or higher power mode or setting as used hereinrefer to power exceeding 90 watts (e.g., ≥100 W, 150 W, 300 W, 450 W)and the terms lower power or low power mode or setting as used hereinrefer to power ≤90 watts.

The PSE (e.g., route processors 13 or any routing device (e.g., networkdevice (router, switch) operable to route, switch, or forward data) maybe in communication with any number of PDs (e.g., line card 12, fabriccard, or other optics card) via cables 17. The PSE 13 may be configuredto deliver power at one or more output levels (e.g., programmable PoE).

The cables 17 are configured to transmit both power and data from thePSE 13 to the PDs 12. The cables 17 may be formed from any materialsuitable to carry both power and data. The cables 17 may comprise, forexample Catx cable (e.g., category 5 twisted pair (e.g., four-pair)Ethernet cabling) or any other type of cable. The cables 17 may bearranged in any configuration. The cable 17 may be rated for one or morepower levels, a maximum power level, a maximum temperature, oridentified according to one or more categories indicating acceptablepower level usage, for example. In one example, the cables 17 correspondto a standardized wire gauge system such as AWG (American Wire Gauge).

In order to support cable systems operating above and beyond 100 Wsystems, an RJ45 connector (e.g., modified RJ45 or similar connector) atports 14 and 20 are integrated with a resistor network that identifiescable systems specifically designed for 150 W, 300 W, 450 W (or otherpower level), and greater power, including lengths from 5 meters up toabout 50 meters (or other suitable lengths), as appropriate for adefined cable system. As shown in the expanded view of the connector atports 14, 20 in FIG. 1 and described in detail below, each connector mayinclude a jack (port) 14, 20 mated to a plug 21 comprising one or moreresistors. A cable system comprises the cable 17 with the plug 21 ateach end comprising one or more resistors. Defined resistor settings maybe used to identify that a cable system is acceptable for a particularlevel of power. In the case of a mismatch, the system is prohibited fromoperating above 90 W (or other low power limit).

As described further below with respect to FIG. 3, one or more resistorsmay be integrated into the plug side of the connector and a monitoringcircuit placed on a jack side of the connector. The resistor may be abuilt in resistor or resistor cap for the connector on the cable sidefor auto detection, for example. Available amperage to the wires isdetermined by the resistor settings in the plug, as described below withrespect to FIG. 4. The system insures that the appropriate cable wireampacity and plug combination is correctly sized for the powerapplication desired. If the system does not detect a resistor at bothends of the cable 17 or a mismatch is found between resistors, power atthe PSE 13 may be adjusted to a lower power setting to prevent damage tothe cable/connector system.

In one or more embodiments, an OIR (Online Insertion and Removal) button(also referred to as an online removal button) may be integrated intothe connector system (jack 14, 20) to prevent unintended cable removalbefore lowering the current, as well as to prevent arcing on theconnector system during extraction under power. As described below withrespect to FIGS. 6A-6C, the OIR system provides for graceful softwareshutdown at the powered device and a means to disable (or reduce)current flow on the wires to prevent arcing and other forms ofelectrical disruption to the connector system.

It is to be understood that the PoE system shown in FIG. 1 is only anexample, and other arrangements (e.g., number of route processors 13,PSUs 16, line cards 12, or downlink/uplink ports 14, 20) may be usedwithout departing from the scope of the embodiments. Furthermore, theconnectors (jacks, plugs), cables, cable lengths, and power rangesdescribed herein are only examples and other types of connectors,lengths of cable, type of cable systems, or power levels may be usedwithout departing from the scope of the embodiments.

FIG. 2 is a flowchart illustrating an overview of a process forverification of cable application in power over communications systems,in accordance with one embodiment. As previously noted, resistors areintegrated into a plug portion of a connector attached to each end of acable and a monitoring circuit is placed on the jack side of theconnector, with available amperage to the wires determined by theresistor settings in the plug. At step 22, the monitoring circuitidentifies insertion of the plug at a port of the PSE (e.g., plug 21attached to cable 17 received in mating jack 20 at port 14 of the PSE 13in FIG. 1). The system checks for the presence of a resistor at theplugs at each end of the cable (step 23). If no resistor is found acrossany pair, the connector and cable system is assumed to handle only lowpower operation (e.g., 90 W maximum) (steps 24 and 25). The system onlyoperates in low power operation and high power operation is blocked.

When matching resistors are detected at each end of the cable on atleast one of the four pairs, the cable system may be identified asconfigured to handle higher power operation (e.g., ≥100 W) (steps 26 and28). If only one of the two resistors in a pair is detected or aresistor pairing mismatch occurs, the cable system is assumed to handleonly low power operation (e.g., 90 W maximum) (steps 26 and 25).

As described below with respect to FIG. 4, a specific power level or aspecific power level for a specified length of cable may be indicated bythe number of resistors or locations of resistors within the plugs (endsof cable). For example, a single matched pair of resistors may indicatedifferent power levels based on the pair of wires on which the resistoris connected. In another example, when two or more matching resistors ineach end of the cable are detected across the four pairs, the cablesystem is assumed to handle xxx Watts (wherein xxx depends on the wiregauge of the cable). For example, for a 22 AWG cable, xxx may be 600 Wand the cable has a resistor network setting specific for that gaugewire, for 24 AWG cable, xxx may be 300 W and the cable has a resistornetwork setting for that gauge wire. This allows for future cableampacity beyond the intended 300 W. It also allows for an intermediarypower delivery of 150 W systems, or another optimal power level.Resistors may also be connected across different pairs to provide moresetting variables.

It is to be understood that the process shown in FIG. 2 and describedabove is only an example and that steps may be combined, added, removed,reordered, or modified without departing from the scope of theembodiments. Also, it is to be understood that the resistorconfigurations and power levels described above are only examples.

FIG. 3 illustrates an example of a circuit for use in higher power PoEcable/connector auto compliance verification, in accordance with oneembodiment. As previously described, the circuit performs resistordetection to determine cable capability, for each pair of wires at aport. For simplification, the circuit is shown for only one of the fourpairs of wires at one of the ports. The circuit shown in FIG. 3 alsoincludes optional fault detection components to check for pair-to-pairimbalance or other faults. The circuit shown in FIG. 3 operates betweenpower source 31 and a connector (jack 32, plug 33) at the port. Thesource 31 may provide, for example, 58VDC or other suitable power level,as previously described. The connector may comprise, for example, anRJ45 (or similar) connector for providing power and data over a cable tothe powered device (e.g., line card 12 in FIG. 1).

A microcontroller 34 (e.g., PIC (Programmable Interface Controller)) maybe used to compare all four pairs and provide an indication of an out ofbalance condition or fault and initiate an alarm. A power detectionmodule 35 checks the resistors at each end of the cable, identifies thepower capability of the cable system, and determines if the correctconnector is installed. The controller 34 and power detector maydetermine the proper power output level (e.g., 90 W, 150 W, 300 W, orother suitable power level) and directs the source 31 to operate at anappropriate power level based on the capability of the cable system. Thepower detection module 35 may also perform one or more functions of theonline removal module described below with respect to FIGS. 5, 6B, and6C.

Power passes from the source 31 through resistors 36, which are incommunication with differential amplifiers 37. The circuit includesfield effect transistors (FETs) 38 receiving input from the source 31(via the resistors 36) and the controller 34, and providing input toinductors 39 through inline diodes 40. The inductors 39 may define, forexample, a transformer with a single input provided to both inductors.The controller 34 also receives input from a rise and fall detector 42tapped into Ethernet lines. The Ethernet circuit includes Ethernetmagnetics 43 and DC blocks 44. Temperature of the cable (wires, pair ofwires) may also be provided to the controller 34 via detector 41 foradditional fault detection. The temperature may be calculated in eachwire, each pair of wires, the four-pair cable, or any combination.Thermal modeling of the cable may be performed as described in U.S.Patent Application No. 15/604,344, entitled “Thermal Modeling for CablesTransmitting Data and Power”, filed May 24, 2017, for use in faultdetection, for example.

The power detect module 35 (e.g., circuits, components) or one or morecomponents of the power detection system may also be located at the jack32.

In order to avoid the use of large magnetics to handle both data andpower, the system may use passive coupling instead of integratedmagnetics for data transfer. For example, the system may use AC couplingrather than passing through the Ethernet magnetics 43. This avoids theuse of large magnetics to handle both data and power. Capacitors may beused to block the DC power from the Ethernet magnetics to prevent ashort. In one example, capacitors are used inline and inductors are usedto deliver power with matched power inductors.

It is to be understood that the circuit show in FIG. 3 and describedabove is only an example and other components or arrangement ofcomponents may be used to provide cable capability detection, faultdetection, or power management, without departing from the scope of theembodiments.

FIG. 4 is a table illustrating an example of a cable/connector autocompliance verification system, in accordance with one embodiment. Theresistor detection system may be connected across any, some, or all ofthe four pairs of wires. In order to create more fields in the resistormatrix, resistors may also cross pairs (e.g., wires 1 and 3, wires 5 and6, etc.). This allows for several other variables in custom cablesolutions. In the example shown in the table of FIG. 4, a 1 mohmresistor is used in the same pairing position on each connector plug ofthe cable (both ends of the cable). In one example, the network may beterminated across different pairs to indicate available powerdistribution. Resistors may also be located in more than one pair toindicate additional cable performance parameters (e.g., other powerlevels (TBD (to be decided)). A pulse train detection method may be usedat a first interconnect to determine cable type.

The resistor system in the plug at each end of the cable may be used inseveral ways, in addition to providing the ampacity of the plug andcable for a specific application. For example, temperature rating, datarating, and length may be incorporated into the resistor matrix toindicate other factors to the control system for use in determining whenan error has occurred. If a temperature is measured beyond the rating ofthe cable, an error may be generated.

The higher power PoE system may operate at a current level that maycause damage (e.g., pitting, high temperature, surface alterations) ifthe plug is removed from the jack while under load. At power exceeding100 W on the PoE jack, the per pin ampacity may go from 500 ma nominalto 2000 ma nominal, which is a significant amount of current todisconnect. If the plug is removed from the jack while under full loadsignificant damage may occur at the connector, with more damageoccurring with each removal under load. This may cause the plug/jackconnector system to be destroyed after ten disconnects, for example.

If a safety monitoring system operating within a 10 ms loop, forexample, monitors the integrity of each wire, current to all connectorpins will be turned off by the 11 ms point in the safety loop scanningthrough all 8 wires. During removal of the connector system, as soon asone wire is detected to be removed, all current is set to off. In thismethod, relying on the safety function to terminate current in theconnector system, the pins in the connector system have basicprotection, but may not be guaranteed protection from damage. Asdescribed below, an online removal button (e.g., mechanical plunger,switch, touch button) may be used to provide no-load (or reduced load)cable removal.

FIG. 5 is a flowchart illustrating an overview of a process for reducedload cable removal, in accordance with one embodiment. In one or moreembodiments, an OIR momentary button is placed in the RJ45 connectorsystem (as shown below in FIG. 6B). The button is pressed when a userwants to remove a cable and an indication of OIR activation is receivedat an OIR module (online removal module) at the network device (e.g.,route processor 13 in FIG. 1) (step 50). Software and/or hardwaremonitor activation of the button and alert the powered device viaEthernet packets on the cable to gracefully shut down (step 52). Whenthe current monitors in the PSE detect that all pairs have base levelpower (e.g., ≤90 W, low power setting, reduced current), it is safe toremove the cable (steps 54 and 56). The corresponding port at the PSEmay be shut down. Also, LEDs (described below) flashing or solid duringthe time after which the OIR button is pressed may move to an off stateto indicate that it is safe to remove the cable. Maintenance personnelmay then remove the cable without any damage to the connector. The OIRbutton may be pressed at either end of the cable (e.g., jack at PSE portor jack at PD port).

It is to be understood that the flowchart shown in FIG. 5 and describedabove is only an example and that steps may be modified or added,without departing from the scope of the embodiments.

FIGS. 6A, 6B, and 6C illustrate examples of an OIR system that providesfor indication of cable power compatibility and/or reduced load cableremoval, in accordance with one or more embodiments. FIG. 6A shows anRJ45 type jack 60 comprising an opening 61 for receiving a plugconnected to a cable. The jack 60 comprises three LED (Light-EmittingDiode) indicators 62 a, 62 b, and 62 c (e.g., red, green, yellow). Thered LED illuminates when the cable system is unable to support themaximum per wire ampacity. For example, if a cable system is insertedinto the jack 60 and based on its resistors (e.g., mismatch, missing aresistor at one plug, no resistors) the cable system is not capable ofdelivering higher power PoE (e.g., power level exceeding 90 W), thesystem illuminates the red LED 62 a.

FIG. 6B shows an RJ45 type jack 63 comprising an additional OIR (onlineinsertion and removal) momentary push button (switch) 64 along withindicator light 62 a on a face 67 of the port. The online removal button64 allows the user to indicate to system software the user's intent toremove a cable. As described above with respect to the flowchart of FIG.5, the powered device is notified of the intent to remove power uponactivation of the button 64. In one example, the LED 62 a begins toflash and the powered device gracefully shuts down. Power is thendisconnected, predicated on the current monitors showing that all pairshave base level power (e.g., 90 W or less). The LED indicator 62 a isthen turned off to indicate that it is safe to remove the cable(cable/plug assembly).

The online removal button 64 may comprise any type of mechanical buttonor switch that may be depressed or otherwise actuated, a touch sensitivebutton that provides activation of an electrical switch, or any othertype of device that is selectable by a user to initiate transmittal of asignal to an online removal module operable to reduce power at a PSEport.

FIG. 6C illustrates a jack 65 configured with additional space to allowfor test and LED indicators 66 a, 66 b, 66 c. In one example, one LEDlights up to indicate 90 W or less capability, another signifies 150 Wor less capability, and another LED indicates 300 W or less capability.More LEDs may be added for wattage requirements above 300 W. Also,different combinations of LEDs may indicate other power levels. Theadditional size of the jack 65 allows for improved connector pinassemblies to dissipate ampacity to 3 amps per pin at temperatures to90° C., for example.

It is to be understood that the jack configurations shown in FIGS. 6A-6Care only examples and that other configurations may be used withoutdeparting from the scope of the embodiments. For example, the jack mayinclude any number of indicator lights with the online removal button 64or just the online removal button with no indicator lights.

In one or more embodiments, the button (switch) 64 may be designed suchthat once depressed, it remains depressed until the cable is removed andthen another cable or the same cable is re-inserted. The button 64 maythen automatically move to its extended position, waiting for the nextOIR of the cable. The button 64 may act as a locking mechanism that willretain the RJ45 plug and prevent it from being removed. In one example,a cable is not allowed to be removed under load conditions and withoutsoftware/hardware functionality gracefully shutting down the port andthe powered device.

It is to be understood that the connectors, cables, and power rangesdescribed herein are only examples and that other types of connectors,plugs, jacks, cables, cable systems, or power levels may be used withoutdeparting from the scope of the embodiments.

The embodiments described herein operate in the context of a datacommunications network including multiple network devices. The networkmay include any number of network devices in communication via anynumber of nodes (e.g., routers, switches, gateways, controllers, accesspoints, or other network devices), which facilitate passage of datawithin the network. The network devices may communicate over or be incommunication with one or more networks (e.g., local area network (LAN),metropolitan area network (MAN), wide area network (WAN), virtualprivate network (VPN) (e.g., Ethernet virtual private network (EVPN),layer 2 virtual private network (L2VPN)), virtual local area network(VLAN), wireless network, enterprise network, corporate network, datacenter, Internet of Things (IoT), Internet, intranet, or any othernetwork).

FIG. 7 illustrates an example of a network device 70 (e.g., PSE, PD,transport system, route processor card chassis in FIG. 1) that may beused to implement the embodiments described herein. In one embodiment,the network device 70 is a programmable machine that may be implementedin hardware, software, or any combination thereof. The network device 70includes one or more processors 72, memory 74, interface 76, andresistor detection/OIR module (online removal module) 78.

Memory 74 may be a volatile memory or non-volatile storage, which storesvarious applications, operating systems, modules, and data for executionand use by the processor 72. For example, components of the resistordetection/OIR module 78 (e.g., code, logic, or firmware, etc.) may bestored in the memory 74. The network device 70 may include any number ofmemory components.

The network device 70 may include any number of processors 72 (e.g.,single or multi-processor computing device or system), which maycommunicate with a forwarding engine or packet forwarder operable toprocess a packet or packet header. The processor 72 may receiveinstructions from a software application or module, which causes theprocessor to perform functions of one or more embodiments describedherein.

Logic may be encoded in one or more tangible media for execution by theprocessor 72. For example, the processor 72 may execute codes stored ina computer-readable medium such as memory 74. The computer-readablemedium may be, for example, electronic (e.g., RAM (random accessmemory), ROM (read-only memory), EPROM (erasable programmable read-onlymemory)), magnetic, optical (e.g., CD, DVD), electromagnetic,semiconductor technology, or any other suitable medium. In one example,the computer-readable medium comprises a non-transitorycomputer-readable medium. Logic may be used to perform one or morefunctions described above with respect to the flowcharts of

FIGS. 2 and 5, or other functions such as power level negotiations orsafety subsystems described herein. The network device 70 may includeany number of processors 72.

The interface 76 may comprise any number of interfaces or networkinterfaces (line cards, ports, connectors) for receiving data or power,or transmitting data or power to other devices. The network interfacemay be configured to transmit or receive data using a variety ofdifferent communications protocols and may include mechanical,electrical, and signaling circuitry for communicating data over physicallinks coupled to the network or wireless interfaces. For example, linecards may include port processors and port processor controllers. Theinterface 76 may be configured for PoE, enhanced PoE, PoE+, UPoE, orsimilar operation.

It is to be understood that the network device 70 shown in FIG. 7 anddescribed above is only an example and that different configurations ofnetwork devices may be used. For example, the network device 70 mayfurther include any suitable combination of hardware, software,algorithms, processors, devices, components, or elements operable tofacilitate the capabilities described herein.

Although the method and apparatus have been described in accordance withthe embodiments shown, one of ordinary skill in the art will readilyrecognize that there could be variations made to the embodiments withoutdeparting from the scope of the invention. Accordingly, it is intendedthat all matter contained in the above description and shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. A method for verifying operation of a cable forPower over Ethernet applications, comprising: identifying insertion of aplug at a port of power sourcing equipment for delivery of Power overEthernet, the plug connected to one end of a cable with another plugconnected to an opposite end of the cable; checking for resistors ateach of the plugs; determining a power rating of the cable based on theresistors located at the plugs; and powering the port to a power levelbased on said power rating.
 2. The method of claim 1 wherein poweringthe port comprises powering the port to provide at least 100 watts powerto a powered device.
 3. The method of claim 1 wherein checking forresistors at each of the plugs comprises checking for matching resistorsat each of the plugs.
 4. The method of claim 1 wherein checking forresistors comprises checking for resistors in each pair of a four-paircable.
 5. The method of claim 1 wherein no resistor is found in at leastone of the plugs and powering the port comprises powering the port to amaximum of 90 watts.
 6. The method of claim 1 further comprisingmonitoring a temperature of the cable and reducing said power level ifsaid temperature exceeds a specified limit.